How do I know if the property price is fair in this area?

Start at the micro-location level, not just the broad area.
Ask what nearby alternatives exist, how quality differs, whether the developer profile is stronger or weaker, how efficient the layout is, what the charges look like, and whether the price includes a premium for view, scarcity, or near-term handover.
Sometimes a price looks high but is justified by a genuinely superior product.
In other cases, a lower price hides a weakness in layout, location, or overall asset quality.
Fair pricing is about appropriate value, not simply the lowest number.